1. Field of the Invention
The present invention relates to an image reproducing apparatus and, more particularly, to an image reproducing apparatus for concealing error uncorrectable data of a video signal which is encoded with high efficiency, and reproducing the obtained data.
2. Related Background Art
As a conventional apparatus of this type, a digital VTR for converting a video signal into a digital signal, and recording/reproducing the digital signal is known. In recent years, of such digital VTRs, one which records/reproduces a digital image signal after compression and encoding has been proposed.
As a technique for compressing and encoding an image signal with high efficiency, an orthogonal transform encoding system is known. In this technique, an image signal is divided into blocks each including a plurality of pixels, and each image signal block is subjected to orthogonal transform such as discrete cosine transform. Thereafter, the transformed coefficients are quantized and entropy-encoded.
In a digital VTR which compresses and records an image using this orthogonal transform encoding system, an image signal is encoded and recorded in units of blocks. In a reproduction mode, especially in a special reproduction mode such as a search reproduction mode, recorded image data cannot be normally reproduced. When an error is generated in encoded data, a code error is generated in units of blocks. Since variable length codes are popularly used, a decoding error propagates over a plurality of blocks, resulting in large deterioration of an image.
When image data of a block (to be referred to as an error block hereinafter) which includes undecodable data (to be referred to as error data hereinafter) are interpolated, normally, interframe interpolation and intrafield interpolation are selectively used. More specifically, an interframe correlation (an intrablock sum of difference absolute values between pixels in the current frame and those in the immediately preceding frame) of image data of each of the upper and lower blocks of the error block is calculated to estimate the presence/absence of a movement in the error block. If the presence of a movement is detected, intrafield interpolation is performed; otherwise, interframe interpolation is performed.
However, when such a method is applied to a case wherein the error block corresponds to a high-definition image and includes a movement, intrafield interpolation is selected regardless of whether image data around the error block correspond to a high-definition image. In this case, the intrafield interpolation can provide a strong temporal correlation but weakens a spatial correlation. As a result, the resolution of the interpolated block is lowered, and a low-resolution block is included in a high-definition image, resulting in an unbalanced image.